Automatic document feeding apparatus

ABSTRACT

An automatic document feeding apparatus includes a shaft, an ADF roller for feeding documents piece by piece by cooperating with a separating member, and a power switching member for selectively connecting a driving member with the shaft. The power switching member is installed on the shaft. The ADF roller is also mounted on the shaft such that the ADF roller can rotate by receiving a torque only in a first direction.

This application is a divisional application of co-pending U.S. patentapplication Ser. No. 10/935,166, filed Sep. 8, 2004, which claimsbenefit under 35 U.S.C. §119(a) of Korean Patent Application No.2003-81735, filed on Nov. 18, 2003, in the Korean Intellectual PropertyOffice, the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic document feedingapparatus. More particularly, the present invention relates to anautomatic document feeding apparatus having an automatic documentfeeding (ADF) roller designed to transmit power only in one direction.

2. Description of the Related Art

Generally, a document feeding apparatus in a telecopy machine, a copymachine, a scanner, and a digital compound machine is used to feeddocuments stacked in a feeding base to reading means for reading imageinformation printed or written down on the documents.

FIG. 1 shows a conventional automatic document feeding apparatus. Asshown in the drawing, a conventional automatic document feedingapparatus includes a shaft 2 rotated by driving means (not shown)connected to a gear 3, an ADF roller 3 installed on the shaft 2, andseparating means 4 for separating documents D sheet by sheet. A feedroller 5 for feeding the documents at a predetermined speed is providedon a front end of the ADF roller 3. The feeding speed of the ADF roller3 is identical to or less than that of the feed roller 5. In general,the feeding speed of the ADF roller 3 is slightly less than that of thefeed roller 5. Therefore, when the feed roller 5 starts feeding thedocuments D fed to a feeding base 1 by the ADF roller 3, the document Dmay be torn between the ADF roller 3 and the feed roller 5 due to thedifference in the feeding speed therebetween.

To solve this problem, a clutch (not shown) is provided in the automaticdocument feeding apparatus. That is, when the shaft 2 rotates in a firstdirection where the document D is fed, the clutch is engaged with theADF roller 3 and transmits a torque to the ADF roller 3, and when theshaft 2 rotates in a second direction opposite to the first direction,the clutch is disconnected from the ADF roller and the torque from theshaft 2 is not transmitted. When the feed roller 5 starts feeding thedocument D, the ADF roller 3 rotates faster than the shaft 2. At thispoint, since the shaft 2 is disconnected from the ADF roller 3 by theclutch, the ADF roller 3 can smoothly rotate in response to the feedingspeed of the feed roller 5.

In addition, while the feed roller 5 is feeding the document D, thedocument D may be jammed. In this case, the jammed document D may beremoved by pulling a front end of the document D in a direction A. Atthis point, the jammed document D is removed as the ADF roller 3smoothly slips on the shaft 2. Alternatively, in case of pulling a rearend of the jammed document D to remove the jammed document D, the clutchis operated in an opposite direction such that the ADF roller 3 rotatesthe shaft 2 in the second direction. At this point, since the shaft 2 isconnected to the driving means by a plurality of reduction gears, theADF roller 3 rotates against a relatively large amount of resistance. Asa result, it becomes difficult to remove the jammed document D, and, inthe worst case, the jammed document D may be torn.

The automatic document feeding apparatus may further include a pickuproller 7 for picking up the document D and feeding the same to the ADFroller 3. The pickup roller 7 contacts the document D only when pickingup the document D. That is, when the pickup operation is completed, thepickup roller 7 moves away from the document D. The pickup roller 7 isinstalled on a bracket 8 rotatably coupled on the shaft 2. In order torotate the bracket 8, the driving means should be designed tobi-directionally rotate. However, the direction change of the drivingmeans slows down the document feeding speed, thereby reducing the numberof documents fed per unit of time.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an automatic documentfeeding apparatus that can easily remove a jammed document regardless ofa pulling direction of the jammed document.

Also, embodiments of the present invention provide an automatic documentfeeding apparatus that is designed to prevent the reduction of thedocument feeding speed, which may be caused by a direction change of thedriving means.

According to an aspect of the present invention, there is provided anautomatic document feeding apparatus comprising a shaft; an ADF rollerwhich feeds documents sheet by sheet by cooperating with separatingmeans, the ADF roller being mounted on the shaft such that the ADFroller can rotate by receiving a torque only in a first direction fromthe shaft; and power switching means which selectively connects drivingmeans with the shaft, the power switching means being installed on theshaft.

The automatic document feeding apparatus may further comprise a pickuproller which picks up the documents stacked in a feeding base byreceiving the torque only in the first direction from the shaft; abracket rotatably mounted on the shaft, the pickup roller beinginstalled on the bracket; clutching means which transmits the torque ofthe shaft to the bracket when the shaft rotates in the first directionand does not transmit the torque of the shaft to the bracket when theshaft rotates in a second direction; and an elastic member which biasesthe bracket in the second direction.

According to another aspect of the present invention, the clutchingmeans may comprise a clutch spring fitted on a first cylindricalprojection formed on the shaft and a second cylindrical projectionformed on the bracket by first fitting force to allow the bracket torotate in the first direction, the clutch spring having a first endinserted in a first insertion groove provided on the bracket; a clutchcover which encloses the clutch spring, the clutch cover being providedwith a second groove in which a second end of the clutch spring isinserted and a circumferential projection; and a stopper contacting thecircumferential projection so as to prevent the clutch spring fromrotating in the second direction.

The bracket may be provided with a plurality of the first insertiongrooves for adjusting the first fitting force, and the clutch cover isprovided with a plurality of the second insertion grooves for adjustingthe first fitting force.

The stopper may be provided on the bracket. The power switching means isdesigned to disconnect the driving means with the shaft when thedocument is jammed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic view of a conventional automatic document feedingapparatus;

FIG. 2 is a view of an image information input system where an automaticdocument feeding apparatus according to an embodiment of the presentinvention is employed;

FIG. 3 is a perspective view of an automatic document feeding apparatusaccording to an embodiment of the present invention;

FIG. 4 is a sectional view illustrating a relationship between a shaftand an electronic clutch used as power switching means according to anembodiment of the present invention;

FIGS. 5 and 6 are views illustrating a relationship between a shaft, apickup roller and an ADF roller according to an embodiment of thepresent invention;

FIG. 7 is an exploded perspective view of clutching means according toan embodiment of the present invention;

FIGS. 8 and 9 are side views illustrating an operation of clutchingmeans depicted in FIG. 7; and

FIG. 10 is a view illustrating a relationship between a shaft, pickuproller and ADF roller in the course of removing a jammed documentaccording to an embodiment of the present invention.

In the drawings, like reference numbers are used to refer to likefeatures and structures.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings, in which exemplaryembodiments of the invention are shown. The invention may, however, beembodied in many different forms and should not be construed as beinglimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the concept of the invention to those skilled in theart. In the drawings, the thicknesses of layers and regions areexaggerated for clarity.

FIG. 2 shows an image information input system where an automaticdocument feeding apparatus of the present invention is employed.

As shown in the drawing, there is shown an ADF roller 104 for feedingthe documents D stacked in a feeding base 101 to a feed roller 106 sheetby sheet by cooperating with a separating member 105. The separatingmember 105 is formed of a frictional member biased on the ADF roller 104by an elastic member. By a friction difference between the ADF roller104 and the document D, between the documents D, and between thedocument D and the separating member 105, the documents D can be fedsheet by sheet.

The reference numeral 107 indicates reading means for reading imageinformation printed or written down on the documents D. A contact imagesensor (CIS) or a charge coupled device (CCD) may be used as the readingmeans, among other suitable devices. Reference numerals 109A and 109Brespectively indicate first and second detecting sensors for detectingthe documents D. That is, the first detecting sensor 109A detects thedocuments D picked up from the feeding base 101 to determine starttiming for aligning a front end of the document D on the feed roller106. The second detecting sensor 109B detects the front end of thedocument fed by the feed roller 106 to determine start timing forreading the document by the reading means 107. The second detectingsensor 109B further detects a rear end of the document D to determine ifthe discharge of the document D is completed. The reference numerals 108and 102 respectively indicate a discharging roller and a tray forstacking the documents D discharged by the discharging roller 108. Forstable document feeding, a pickup roller 103 for picking up thedocuments stacked in the feeding base 101 and feeding the same betweenthe ADF roller 104 and the separating member 105 may be furtherprovided. In Particular, when the feeding base 101 is horizontallydisposed, it is preferable that the pickup roller 103 be provided.Reference numeral 100 indicates driving means for driving the feedroller 106, the ADF roller 104 and the pickup roller 103.

FIG. 3 shows the automatic document feeding apparatus according to anembodiment of the present invention.

As shown in the drawing, the shaft 110 is rotated by a driving forcetransmitted from the driving means 100 via a plurality of gears 41 and42. Power switching means 120 is installed on an end of the shaft 110. Abracket 130 is also installed on the shaft 110. The reference numeral140 indicates an elastic member for biasing the bracket 130 in a seconddirection 302.

The power switching means 120 is designed to selectively interconnectthe driving means 100 and the shaft 110. An electronic clutch ispreferable as the power switching means.

FIG. 4 shows a relationship between the shaft 110 and the electronicclutch used as the power switching means 120 according to an embodimentof the present invention.

As shown in the drawing, the electronic clutch includes an electromagnet121 and a gear part 122 slightly spaced away from the electromagnet 121and rotatably installed on the shaft 110. The gear part 122 is connectedto the driving means 100 via the gears 41 and 42 (see FIG. 3). When acurrent is applied to the electromagnet 121, the gear part 122 isattached on the electromagnet 121 by electromagnetic force. Therefore,when the driving means rotates, the electromagnet 121 rotates togetherwith the gear part 122. As shown in FIG. 4, since the electromagnet 121is installed on a cut-away portion 112 of the shaft 110, the shaft 110can rotate together with the electron magnet 121. When the current beingapplied to the electron magnet 121 is cut off, the gear part 122 movesaway from the electromagnet 121. In this state, when the driving meansrotates, only the gear part 122 rotates while the electromagnet 121 andthe shaft 110 do not rotate.

The ADF roller 104 is rotatably installed on the shaft 110. A secondshaft 150 is fixedly or rotatably installed on the bracket 130. Thepickup roller 103 is rotatably installed on the second shaft 150. TheADF roller 104 and the pickup roller 103 are designed to be subject torotational force from the shaft 110 only in a first direction 301 (adocument feeding direction). That is, the ADF roller 104 and the pickuproller 103 rotate in the first direction 301 only when the shaft 110rotates in the first direction 301. When the shaft 110 rotates in thesecond direction 302, the ADF roller 104 and the pickup roller 103 donot rotate.

Referring to FIG. 5, an exemplary structure is shown in which the ADFroller 104 and the pickup roller 103 are designed to receive a torquefrom the shaft 110 only in the first direction 301. A first member 210is coupled on the shaft 110 to rotate together with the shaft 110. Thefirst member 210 is provided with a gear portion 211, a lever portion213 and a pin coupling portion 212. The shaft 110 is provided with a pinhole 113 in which a pin 118 having a length greater than a diameter ofthe shaft 110 is inserted. When the first member 210 is pushed such thatthe pin 113 can be inserted in the pin coupling portion 213, the firstmember 210 is coupled to the shaft 110. Alternatively, the first member210 may be forcedly fitted on the shaft 110. A gear 51 engaged with thegear portion 211 is mounted on the bracket 130. Rotatably coupled to thesecond shaft 150 are a second member 220 having a gear part 221 engagedwith the gear 51 and a lever portion 222. Third members 230 a and 230 bare respectively coupled to the shaft 110 and the second shaft 150 to becapable of sliding in an axial direction thereon. Each of the thirdmembers 230 a and 230 b is provided with a first power coupling portion231 formed in a saw tooth shape defined by opposing sections 233 andinclined sections 234 and a spiral concave portion 232 in which thelever portion 213 (222) is inserted. Each of the ADF roller 104 and thepickup roller 103 is provided with a second power coupling portion 240correspondingly engaged with the first power coupling portion 231, thesecond power coupling portion 240 being formed in a saw tooth shapedefined by opposing sections 241 and inclined sections 242.

When the shaft 110 rotates in the first direction 301, the first member210 coupled on the shaft 110 by the pin 118 rotates in the firstdirection 301 together with the shaft 110. The third member 230 a alsorotates in the first direction 301 with the lever portion 213 contactingan end portion of the spiral concave portion 232. The rotational forceof the shaft 110 is transmitted to the gear portion 221 of the secondmember 220 via the gear portion 211 and the gear 51. The second member220 rotates in the first direction 301 and the third member 230 b alsorotates in the first direction 301 with the lever portion 222 contactingan end portion of the spiral concave portion 232. At this point, whenthe third members 230 a and 230 b rotate in the first direction 301, theopposing sections 233 of the first power coupling portion 231 push theopposing sections 241 of the second power coupling portion 240.Accordingly, the ADF roller 104 and the pickup roller 103 rotate in thefirst direction 301.

Referring to FIG. 6, when the shaft 110 rotates in the second direction302, all of the first to third members 210, 220, and 230 a and 230 brotate in the second direction 302, as a result of which the inclinedsections 234 of the first power coupling portion 231 push the inclinedsections 242 of the second power coupling portions 240 a and 240 b.Therefore, the third members 230 a and 230 b is pushed in an arrowdirection 303 and thereby the first power coupling portion 231 isseparated from the second power coupling portion 240. Accordingly, boththe ADF roller 104 and the pickup roller 103 do not rotate.

When the shaft 110 rotates in the first direction 301 again, the leverportions 213 and 222 of the first and second members 210 and 220 pushthe spiral concave portions 232 of the third members 230 a and 230 bsuch that the third members 230 a and 230 b slide in the direction ofarrow 304 in FIG. 5, thereby the first power coupling portion 231 iscoupled to the second power coupling portion 240. Accordingly, as shownin FIG. 5, both the ADF roller 104 and the pickup roller 103 rotate inthe first direction 301.

In order to reduce load in the course of feeding the documents D, thepickup roller 103 is preferably designed to contact the documents onlywhen it picks up the documents D. The pickup roller 103 is installed onthe bracket 130 rotatably mounted on the shaft 110. Clutching means 250is disposed between the bracket 130 and the shaft 110 for transmittingrotational force of the shaft 110 to the bracket 130 when the shaftrotates in the first direction and for interrupting rotational force ofthe shaft 130 when the shaft 110 rotates in the second direction 302 soas not to transmit the rotation force to the bracket 130.

FIG. 7 shows the clutching means 250 of FIG. 3 in detail. As shown inthe drawing, the bracket 130 is provided at a sidewall 131 with a firstcylindrical projection 133 defining an insertion portion 132 in whichthe shaft 110 is inserted. The bracket 130 is further provided at thesidewall 131 with a first insertion portion 134 in which a first end 271of a clutch spring 270 is inserted and a stopper 135. The shaft 110 isprovided with a pin hole 113. A fourth member 260 provided with a secondcylindrical projection 261 and a pin coupling portion 262 are insertedaround the shaft 110. The fourth member 260 is coupled on the shaft 110through a substantially identical manner to the first member 210 ofFIGS. 5 and 6. Alternatively, the fourth member 260 may be forcedlyfitted around the shaft 110. A clutch cover 280 formed in a hollow shapeis disposed enclosing the clutch spring 270. The clutch cover 280 isprovided with a second insertion groove 281 in which a second end 272 ofthe clutch spring 270 is inserted and an outer circumferentialprojection 282 contacting the stopper 135. The clutch spring 270 isfitted on the first and second cylindrical projections 133 and 261.Since an inner diameter of the clutch spring 270 is less than outerdiameters of the first and second cylindrical projections 133 and 261,the clutch spring 270 is inserted around the projections 133 and 261while being slightly widened. Therefore, the clutch spring 270 biasesthe first and second cylindrical projections 133 and 261 using a firstfitting force.

When the shaft 110 rotates in a first direction, the rotational force ofthe shaft 110 is transmitted to the first cylindrical projection 133 bythe first fitting force of the clutch spring 270 via the secondcylindrical projection 261. The first end 271 of the clutch spring 270is inserted in the first insertion groove 134 to push the bracket 130 inthe first direction 301 (see FIG. 3). Accordingly, as shown in FIG. 8,the bracket 134 rotates in the first direction 301 and the pickup roller103 contacts the document D. The pickup roller 103 and the ADF roller104 rotate in the first direction 301 as described with reference to theFIG. 6.

The first fitting force of the clutch spring 270 should be set such thatit can rotate the bracket 130 in the first direction 301 whileovercoming an elastic force of the elastic member 140 when the shaft 110rotates in the first direction 301. To set the first fitting force ofthe clutch spring in response to this requirement, the bracket 130 andthe clutch cover 280 may be provided with a plurality of insertiongrooves 134 and 281, respectively. That is, by properly inserting thefirst and second ends of the clutch spring 270 in the first and secondinsertion grooves 134 and 281, respectively, the first fitting force canbe adjusted.

When the shaft 110 further rotates in the first direction 301 after thepickup roller 103 contacts the document D, the bracket 130 is biased tofurther rotate in the first direction 301. At this point, the first end271 of the clutch spring 270 receives repulsive force from the bracket130 in the second direction 302. At this point, the first fitting forceof the clutch spring 270 is reduced as the inner diameter of the clutchspring 270 is widened in a moment. As a result, the clutch spring 270slips on the first cylindrical projection 133. Accordingly, even whenthe shaft 110 further rotates in the first direction 301 after thepickup roller 103 contacts the document D, the pickup roller 103maintains its gentle contacting state without applying excessivepressure to the documents D.

When a predetermined time has elapsed after the front end of thedocument D is detected by the first detecting sensor 109A, the documentD is fed by the feed roller 106. When the document D is fed, since thereis no need of rotating the shaft 110, the current being applied to thepower switching means 120 is cut off to disconnect the driving means 100from the shaft 110, thereby stopping the rotation of the shaft 110. Thebracket 130 rotates in the second direction 302 by the elastic force ofthe elastic member 140 to separate the pickup roller 103 from thedocument D. At this point, the first end 271 of the clutch spring 270 ispushed in the second direction 302 while bracket 130 rotates in thesecond direction 302. Then, the first fitting force of the clutch spring270 is reduced as the inner diameter of the clutch spring 270 iswidened, and thereby the clutch spring 270 slips on the firstcylindrical projection 133. Accordingly, the bracket 130 smoothlyrotates in the second direction 302. As shown in FIG. 8, it ispreferable that there is provided suppressing means 160 for suppressingthe excessive rotation of the bracket 130 in the second direction 302.

When the shaft 110 rotates in the first direction 301 by the drivingmeans 100, the bracket 130 rotates in the first direction 301 to allowthe pickup roller 103 to contact the document D. The document D pickedup by the pickup roller 103 is fed sheet by sheet while passing throughbetween the ADF roller 104 and the separating means 105. When a frontend of the document D is advanced to the feed roller 106, the document Dis conveyed by the feed roller 106. Accordingly, there is no need forbi-directionally rotating the driving means 100 and preventing the delayof the feeding time, which is incurred in the conventional automaticdocument feeding apparatus.

A feeding speed of the ADF roller 104 is identical to or less than thatof the feed roller 106. In general, the feeding speed of the ADF roller104 is slightly less than that of the feed roller 106. Therefore, toprevent the document D from being torn by the difference in the feedingspeed, since the ADF roller 104 should rotate in response to the feedingspeed of the feed roller 106, the ADF roller 104 should be disconnectedwith the shaft 110. Referring to FIG. 9, when the ADF roller 104 rotatesin the first direction 301 at the feeding speed identical to that of thefeed roller 106, the inclined sections 242 of the second power couplingportion 240 push the inclined sections 234 of the first power couplingportion 231 and the third member 230 a is pushed in the direction ofarrow 303. As a result, the power connection between the shaft 110 andthe ADF roller 104 is cut off and the ADF roller 104 smoothly rotates inresponse to the feeding speed of the feed roller 106.

To align the front end of the document D on the feed roller 106, thefeed roller 106 does not rotate or rotates in the second direction untilthe front end of the document D reaches thereto. That is, in a statewhere the feed roller 106 is stopped or rotates in the second direction302, the document D is conveyed from the first detecting sensor 109A toslightly over the feed roller 106 after the front end of the document Dis detected by the first detecting sensor 109A. As a result, as shown bya broken line 305 of FIG. 2, the document D is neatly curved and alignedon the feed roller 106. In this state, when the feed roller 106 rotatesin the first direction 301, the document D is advantageously stably fedwithout being skewed.

Power switching means that is identical to that shown in FIG. 4 can befurther provided on the feed roller 106. In this case, the currentapplied to the power switching means can be cut off to prevent the feedroller 106 from rotating while the document D is being aligned on thefeed roller 106. After the document alignment is finished, the currentis applied to the power switching means to convey the document byrotating the feed roller 106.

For the automatic document feeding apparatus that does not employ thealigning process, The ADF roller 104, the pickup roller 103 and the feedroller 106 are continuously rotated only in the first direction 301. Atthis point, after the front end of the document is inserted in the feedroller 106, the power switching means disconnects the driving means 100from the shaft 110. As a result, the bracket 130 rotates in the seconddirection 302 by the elastic force of the elastic member 140 to allowthe pickup roller 103 to be separated from the document D and the ADFroller 104 rotates in response to the feeding speed of the feed roller106.

When the document D is jammed while being conveyed, a jammed locationcan be identified by checking the first and second detecting sensors109A and 109B. That is, when the front end of the document D is notdetected by the first detecting sensor 109A for a predetermined timeafter the ADF roller 104 and the pickup roller 103 start rotating, itcan be determined that the document D is jammed between the ADF roller104 and the feed roller 106. When the front end of the document D is notdetected by the second detecting sensor 109B for a predetermined timeafter the front end of the document D is detected by the first detectingsensor 109A, it can be determined that the document D is jammed betweenthe feed roller 106 and the reading means 107. When the rear end of thedocument D is not detected by the second detecting sensor 109B for apredetermined time after the front end of the document D is detected bythe second detecting sensor 109B, it can be determined that the documentD is jammed between the reading means 107 and the discharging roller108.

When it is determined that the document D is jammed between the readingmeans 107 and the discharging roller 108, since this is the case wherethe front end of the document D reaches the tray 102, the jammeddocument D can be removed by pulling the document D in a direction A(FIG. 2). When it is determined that the document D is jammed betweenthe feed roller 106 and the reading means 107, it is impossible to pullthe front end of the document D in the direction A. Accordingly, it ispossible to remove the jammed document D by pulling the rear end of thedocument D in a direction B. When the document D is jammed between theADF roller 104 and the feed roller 106, it is possible to remove thejammed document D by pulling the rear end of the document D in thedirection B.

In more in detail, when the rear end of the jammed document D is pulledin the direction B to remove the jammed document D between the feedroller 106 and the reading means 107 or between the ADF roller 104 andthe feed roller 106, the ADF roller 104 rotates in the second direction302. At this point, as shown in FIG. 10, the opposing sections 241 ofthe second power coupling portion 240 push the opposing sections 233 ofthe first power coupling portion 231 in the second direction 302 and thethird member 230 rotates in the second direction 302. As a result, thefirst member 210 and the shaft 110 also rotate in the second direction302. Here, the operation of the clutching means 250 for selectivelyconnecting the bracket 130 with the shaft 110 is important. When theshaft 110 rotates in the second direction 302, the bracket 130 cannotrotate in the second direction 302 by the suppressing means 160. In thiscase, since the first end of the clutch spring 270 is inserted in thefirst insertion groove 134, it is twisted in a direction where thediameter thereof reduces, thereby further biasing the first and secondcylindrical projections 133 and 261. As a result, the shaft 110 and theADF roller 104 cannot rotate in the second direction 302 as far as thebracket 130 does not rotate in the second direction 302. Since thedocument D is pressed between the ADF roller 104 and the separatingmember 105, it is difficult to remove the document D if the ADF roller104 does not rotate. Therefore, when the document D is pulled in thedirection B by excessive force, the document D may be torn.

However, in the present invention, when the shaft 110 rotates in thesecond direction 302, the second end of the clutch spring 270 pushes thesecond insertion groove 281 to rotate the clutch cover 280 in the seconddirection 302. At this point, since the outer circumferential projection282 of the clutch cover 280 contacts the stopper 135, the clutch cover280 cannot rotate. In this state, when the second end 272 of the clutchspring 270 continuously pushes the clutch cover 280 in the seconddirection 302, the inner diameter of the clutch spring 270 is widened.As a result, since there is a slip between the second cylindricalprojection 261 and the clutch spring 270, the torque of the shaft 110 isnot transmitted to the bracket 130. Accordingly, when the jammeddocument D is pulled in the direction B, the jammed document D can beeasily removed while the ADF roller 104 and the shaft 110 smoothlyrotate in the second direction 302. When the document D is jammed, thedriving means 100 is disconnected with the shaft 110 by the powerswitching means 120. As a result, since only the ADF roller 104 and theshaft 110 rotate, the jammed document D can be more easily removed.

According to the above-described automatic document feeding apparatus,the jammed document D can be easily removed and the number of documentsD fed per time can be increased.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. An automatic document feeding apparatus comprising: a shaft; an ADFroller which feeds documents sheet by sheet by cooperating withseparating means, the ADF roller being mounted on the shaft such thatthe ADF roller can rotate by receiving a torque only in a firstdirection from the shaft; power switching means which selectivelyconnects driving means with the shaft, the power switching means beinginstalled on the shaft; and power coupling means comprising a firstcoupling portion that slides axially on the shaft to selectively couplethe shaft to the ADF roller.
 2. The automatic document feeding apparatusof claim 1, wherein the power coupling means further comprises opposingsaw tooth shape members.
 3. The automatic document feeding apparatus ofclaim 2, wherein the power coupling means further comprises a spiralconcave portion in which a lever is inserted, the lever and spiralconcave portions cooperating to slide said first coupling portion toselectively couple the shaft to the ADF roller.
 4. An automatic documentfeeding apparatus comprising: a shaft; a pickup roller rotated byreceiving a torque from the shaft and picking up a sheet of a documenton a feeding base; a second shaft on which the pickup roller isinstalled; an ADF roller to feed the document picked up by the pickuproller; a separating member engaged with the ADF roller to separate thedocument sheets individually; and a bracket on which the pickup rollerand ADF roller are installed, and wherein the pickup roller rotates byselectively receiving the torque only in a first direction from theshaft.
 5. The automatic document feeding apparatus of claim 4, whereinthe ADF roller rotates by selectively receiving a torque only in a firstdirection from the shaft.
 6. The automatic document feeding apparatus ofclaim 4, further comprising: a first power coupling portion rotated bythe torque; a second power coupling portion installed on at least one ofthe ADF roller and the pickup roller, the second power coupling portionconnected to the first power coupling portion; and wherein one of thefirst power coupling portion and the second power coupling portionslides to engage/separate with/from each other.
 7. The automaticdocument feeding apparatus of claim 6, wherein each of the first powercoupling portion and the second power coupling portion comprises a sawtooth defined by opposing sections and incline sections to selectivelyconnect with each other when the shaft rotates in the first direction.8. The automatic document feeding apparatus of claim 4, wherein when theshaft rotates in the first direction, the torque of the shaft istransferred to the bracket and when the shaft rotates in a seconddirection, the torque of the shaft is not transferred to the bracket. 9.The automatic document feeding apparatus of claim 8, wherein the bracketis rotatable with respect to the shaft.
 10. The automatic documentfeeding apparatus of claim 9, further comprising an elastic member whichbiases the bracket to rotate in the second direction.